The present invention relates to a pair of refractory plates for use in a swivelling or rotary sliding closure unit or slide gate, particularly for controlling the discharge of molten metal from a metallurgical vessel, more particularly for casting of molten steel. The present invention more particularly relates to such a pair of refractory plates including a stationary bottom plate having a discharge opening and adapted to be mounted beneath a vessel with the discharge opening aligned with an outlet opening of the vessel, and a movable plate having two discharge openings, the movable plate being mounted for sliding movement with respect to the bottom plate about a center of rotation between a closed position, whereat neither of the discharge openings of the movable plate are aligned with the discharge opening of the bottom plate, and alternate open positions, whereat respective of the discharge openings of the movable plate are in alignment with the discharge opening of the bottom plate, the discharge openings of the movable and bottom plates being centered on a common circular arc centered about the center of rotation, and the discharge openings of the movable plate being positioned symmetrically on opposite sides of the discharge opening of the bottom plate in the closed position. The present invention also is directed to a novel method of operation of such pair of refractory plates.
An example of this type of structure is shown in West German DE-PS No. 28 40 171, wherein there are a pair of refractory plates employed in a closing mechanism for the bottom nozzle of a ladle, and wherein discharge openings of the sliding or movable plate are moved, as required, from opposite sides to align with the discharge opening of the bottom plate and the outlet opening of the ladle. This arrangement results in a premature wear of the bottom plate compared with the movable plate, since the closing or throttling operations of the discharge of the molten metal are achieved by two discharge openings in the movable plate and by only a single discharge opening in the bottom plate. Therefore, the bottom plate must be replaced much more frequently than the movable plate, and this requirement is detrimental to continuous operation.
Additionally, West German DE-PS No. 24 04 425 discloses a rotary slide valve with a central plate assigned to the stationary bottom plate and having a plurality of discharge openings that can be positioned beneath the outlet opening of a vessel, regardless of the closing and opening operation of the movable plate and which acts as the actual bottom plate with discharge openings which can be alternated after wear. The central plate is adjusted by an expensive and complicated drive mechanism which results in this arrangement not being satisfactory for all operating conditions.